search engine considers canonical in different ways.
(1) Mass use of the canonical tag.
(2) Canonical tag pointing to itself in a same page.
How does each engine differ?
(1) - Google doesn't punish you if you are using the canonical tag on hundreds or thousands of your site pages,
- Bing says the tag is less to good.
(2)- Google doesn't care if you link a canonical tag to the same page (i.e. a redirect back to the redirect),
- Bing does and says don't do it.
For Example: Add a rel="canonical" link to the <head> section of each HTML page.
<link rel="canonical" href="URL"/>